1. Field of the Invention
The present invention relates to a heat exchanger used for refrigerators and air conditioners using a refrigerant mixture as an operating fluid, and more specifically, to a condenser, an evaporator and a heat transfer pipe preferably used for them.
2. Description of the Related Art
A pipe having spiral grooves each composed of a single groove and formed on the inner surface thereof (hereinafter, referred to as a pipe with spiral grooves) as shown in FIG. 17 is used as a heat transfer pipe of a heat exchanger used by conventional refrigerators and air conditioners using a single refrigerant such as HCFC-22 (hydrochlorofluorocarbon-22) and the like as an operating fluid, in addition to a flat pipe.
Although the pipe with spiral grooves has an excellent heat transfer performance to a single refrigerant, when a refrigerant mixture which is considered hopeful as a refrigerant substituting for HCFC-22 is used to the pipe, it cannot achieve such a degree of effect as that to the single refrigerant. FIG. 18 is a graph comparing a condensation heat transfer coefficient when the conventional pipe with spiral grooves uses the single refrigerant with that when the conventional pipe uses the refrigerant mixture. That is, a curve a shows a result of experiment when the single refrigerant was used by the pipe with spiral grooves and a curve b shows a result of experiment when the refrigerant mixture was used by the pipe. As apparent from FIG. 18, the condensation heat transfer coefficient when the refrigerant mixture was used is apparently reduced as compared with the case in which the single refrigerant was used, and this reduction is remarkable when a mass velocity is slow. Note, a mixture composed of 30 wt % of HFC-32 (hydrofluorocarbon 32), 10 wt % of HFC-125 and 60 wt % of HFC-134a was used as the refrigerant mixture in the experiment.
Further, JP-A-3-234302 discloses a pipe with cross grooves composed of two types of grooves or main grooves and auxiliary grooves intersecting the main grooves as a heat transfer pipe to be used to the single refrigerant. Although there are proposed heat transfer pipes having various internal configurations other than the above as heat transfer pipes for the single refrigerant, it has not been conventionally known what type of an internal configuration is most efficient as the configuration of a heat transfer pipe for zeotropic refrigerant mixture.
An object of the present invention is to provide a heat transfer pipe having a high heat transfer performance to the refrigerant mixture.
To achieve the above object, the present invention provides a heat transfer pipe used for a condenser and an evaporator in a refrigerating cycle using a refrigerant mixture, the heat transfer pipe comprising main grooves and auxiliary grooves each formed on the inner surface of the heat transfer pipe with the main grooves intersecting the auxiliary grooves, wherein a length of ribs, which are divided into sections by the auxiliary grooves, of ridges formed along the direction of the main grooves is made longer than a width of the ridges, a width of the auxiliary grooves is made smaller than the length of the ribs and further the auxiliary grooves are formed in a direction where a pressure gradient in the heat transfer pipe is reduced.
In the heat transfer pipe, the auxiliary grooves may be formed at a spiral angle in a range of xc2x15xc2x0 with respect to a pipe axis and further they are preferably formed substantially in parallel with a pipe axis.
Further, in the heat transfer pipe, convex deformed portions may be formed to each of the ribs of the main grooves to cause a refrigerant flow along the main grooves to bend in the direction of the auxiliary grooves.
Note, in the above respective heat transfer pipes, the main grooves are formed by being inclined at an angle in a range from 7xc2x0 to 25xc2x0 with respect to the pipe axis.
With the above arrangements, since a refrigerant flow is induced so as to be bent in the direction of the auxiliary grooves and taken into the auxiliary grooves of which the width is narrower than the length of the ribs in the heat transfer pipe of the present invention, concentration boundary layers are divided into sections and new concentration boundary layers are formed from the extreme ends of the respective ribs. As a result, a high heat transfer coefficient can be realized to a refrigerant mixture without substantially reducing a heat transfer area.